| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 5.3 | 46 |
| 2015 | 4.8 | 48 |
| 2014 | 5.9 | 49 |
| 2013 | 4.2 | 49 |
| 2012 | 4.3 | 49 |
| 2011 | 5.6 | 60 |
| 2010 | 4 | 63 |
| 2009 | 3.3 | 62 |
| 2008 | 8.4 | 60 |
| 2007 | 8.5 | 57 |
| 2006 | 6.6 | 56 |
| 2005 | 11 | 45 |
| 2004 | 11.2 | 47 |
| 2003 | 8.4 | 47 |
| 2002 | 7.1 | 45 |
| 2001 | 20 | 39 |
| 2000 | 20 | 40 |
| 1999 | 21.2 | 39 |
| 1998 | 57.5 | 21 |
| 1997 | 64.5 | 15 |
| 1996 | 70 | 8 |
| 1995 | 84.4 | 4 |
| 1994 | 306 | 1 |
| 1993 | 113 | 3 |
| 1992 | 84.5 | 4 |
| 1991 | 24.4 | 17 |
| 1990 | 22.1 | 19 |
| 1989 | 12.4 | 23 |
| 1988 | 167.4 | 2 |
| 1987 | 10.2 | 24 |
| 1986 | 15 | 20 |